The present invention relates to a substrate having treated surface layers, on which water drops scarcely attached or from which attached water drops can easily be removed, and a process for producing it.
Various substrates having treated surface layers are used in various fields, and adverse effects brought about by water on the surface of such substrates are problematic.
For example, in transportation equipments such as electric cars, automobiles, ships or aircrafts, the surface of 1) an exterior part such as an outer panel, a window glass, a mirror or a display surface material, 2) an interior part such as an instrument panel, or 3) other articles, is desired to be always clean. If e.g. raindrops, dusts or soils are deposited on the surface of an article in a transportation equipment, or moisture is condensed thereon due to the temperature or humidity in the air, basic functions of the article in a transportation equipment may be impaired in some cases.
Especially in a case where the article for a transportation equipment is an article for which transparency or see-through property is required (such as a window glass or a mirror), a deterioration of the transparency or see-through property due to attachment of e.g. raindrops, dusts or soils, or concentration of moisture, may impair the purpose intended by the article. For example, on a windshield of an automobile, transparency and see-through property may be impaired due to e.g. attachment of e.g. raindrops.
Means to physically remove water drops (such as removal by wiping off or by means of a wiper) may sometimes impart fine scratch marks on the surface of an article. Further, such scratch marks may sometimes be widened by foreign particles accompanying such water drops. Furthermore, it is well known that when moisture is attached to a glass surface, glass components are likely to elute into the moisture, whereby the surface will be eroded, thus leading to so-called scorching. If the surface is strongly polished or abraded to remove such scorching, a fine roughness is likely to form. At the see-through portion made of glass having substantial scorching or a fine roughens on its surface, its basic function is lowered, and scattering of light on its surface tends to result.
Further, moisture is likely to give a hazardous influence to the surface or the inside of e.g. an article for a transportation equipment and to promote damages, soiling, yellowing or corrosion. Otherwise they may induce a change in the electrical characteristics, the mechanical properties or the optical properties of the article for a transportation equipment. Further, the appearance of such an article may be impaired in some cases, and if it is a surface which is directly visually observed or which is directly touched by a person, the impairment in appearance may give a filthy impression.
Adverse effects of this type due to water are problematic not only in the field of articles for transportation equipments but also in various fields including articles for building or building decoration or articles for electric or electronic equipments.
Under these circumstances, it is strongly desired to impart to the substrate surface a characteristic such that water drops scarcely attach to the substrate surface or attached water drops can easily be removed (hereinafter referred to simply as a water drop removal property). Heretofore, to impart a water drop removal property to a surface, surface treating agents for direct application to the surface of an article, such as a silicone wax, a silicone oil made of organopolysiloxane and a surfactant, have been proposed.
JP-A-58-147484, JP-A-60-221470 and JP-A-4-96935 disclose that a polysiloxane and a polysilazane having a perfluoroalkyl group are excellent in water repellency.
However, they are poor in abrasion resistance and weather resistance, and could not be used outdoors for a long period of time. Further, for e.g. a windshield of an automobile or a window glass for building, not only water repellency but also such a characteristic that water drops roll down on its surface (water drop rolling property) is required. However, they do not necessarily have adequate water drop rolling property.
Further, JP-A-10-194784 proposes a water repellent glass which comprises a glass plate, a base film made of a silicon oxide having part of oxygen atoms replaced with hydroxyl groups, and an organic silicon compound containing a fluoroalkyl group.
The above water repellent glass is excellent in abrasion resistance, but is poor in weather resistance practically. Further, the water drop rolling property is not sufficient.
Further, JP-A-7-252472 discloses a water repellency agent containing a co-hydrolyzate of a perfluoroalkyl group-containing organic silicon compound and a hydrolyzable group-containing methylpolysiloxane. This is obtained by co-hydrolyze a perfluoroalkyl group-containing organic silicon compound which is excellent in water repellency and a hydrolyzable group-containing methylpolysiloxane which is excellent in water drop rolling property, in water and a hydrophilic solvent, so as to obtain one which is excellent in both water repellency and water drop rolling property.
However, if the above water repellency agent is coated on a substrate, until it completely gets dry, the perfluoroalkyl group-containing organic silicon compound having a low surface energy tends to move outside the hydrolyzable group-containing methylpolysiloxane having a high surface energy, and no desired water drop rolling property intended by the latter tends to be obtained.
Further, many of surface treating agents which have conventionally been proposed require a pre-treatment accompanying coating, and the coating tends to be nonuniform. Further, the adhesion of the treating agents themselves to the substrate is low, and their water drop removal property can not be maintained for a long period of time. Thus, the range of their application has been limited.
Further, it is desired to develop a means of imparting such water drop removal property not only to substrates to be produced anew but also to substrates which have already been used. In such a case, the surface treating agent must be capable of imparting water drop removal property simply by directly coating such substrates with the surface treating agent at room temperature. For example, when it is attempted to apply a treatment of imparting water drop rolling property to a windshield for an automobile which has already been used, it is impossible to replace the windshield of each automobile from the economical reason, and it is practically impossible to subject the replaced portion to baking after coating. Accordingly, with conventional means using a surface treating agent, such a treatment is difficult.
Under these circumstances, the present invention has been made to overcome the above problems. Namely, the present inventors have conducted studies on a treating agent which will overcome conventional problems, and have found a means of surface treatment which can be applied to a variety of substrates, and which will impart long lasting excellent water drop removal property (water drop rolling property and water repellency). They have further found that said treatment can be carried out easily, and that the substrate thus treated, having water drop removal property, is particularly suitable as a substrate for a transportation equipment. The present invention has been accomplished on the basis of these discoveries.
It is an object of the present invention to provide a substrate which has water drop removal property, which is excellent in abrasion resistance, weather resistance, boilproof property and chemical resistance, and whose characteristics thereby last semipermanently.
The present invention provides a substrate having at least two treated surface layers, wherein the first layer constituting the outermost layer among the treated surface layers is a layer formed by covering with the following composition (I), and the second layer constituting an underlayer in contact with the first layer is a layer formed by covering with the following composition (II):
composition (I):
a composition containing an organic silicon compound of the following formula (1):
composition (II):
a composition containing a fluorine-containing reactive silane compound (II) which forms a surface having a contact angle of at least 100xc2x0 to water: 
wherein each of R1 to R3 is a methyl group or a group of the following formula (2), provided that at least one of R1 to R3 which are contained in one molecule is the group of the following formula (2), R1, a n number of R2""s and R3 may be the same or different, m is an integer of from 1 to 100, and n is an integer of from 0 to 10; 
wherein A is a C2-10 bivalent hydrocarbon group or an oxygen atom, R4 is a C1-10 monovalent hydrocarbon group, Q is an isocyanate group, a chlorine atom or an alkoxy group represented by OR5, provided that R5 is a C1-6 monovalent hydrocarbon group, a p number of R4,s may be the same or different, a (3-p) number of Q""s may be the same or different, and p is an integer of from 0 to 2.
The fluorine-containing reactive silane compound (II) is represented preferably by the following formula (IIA) and/or (IIB): 
wherein each of Z1 and Z2 is an isocyanate group or a hydrolyzable group, provided that a (3-a) number of Z1""s and a (3-b) number of Z2""s may be the same or different, each of R6 and R7 is hydrogen or a C1-21 organic group, provided that a a number of R6""s and a b number of R7""s may be the same or different, Y is a bivalent organic group, provided that at least one of the group of a a number of R6""s, a b number of R7""s and Y is a fluorine-containing organic group, and each of a and b is an integer of from 0 to 2; 
wherein R8 is hydrogen or a C1-21 organic group, provided that a c number of R8""s may be the same or different and at least one of c number of R8""s is a fluorine-containing organic group, Z3 is an isocyanate group or a hydrolyzable group, and c is an integer of from 1 to 3.
The present invention further provides the above substrate having treated surface layers, which further has a third layer constituting an underlayer in contact with the second layer (on the substrate side), wherein the third layer is a layer formed by covering with a composition (III) containing a reactive silane compound (III) containing no fluorine.
The present invention further provides a process for producing the above substrate having treated surface layers, which comprises a step of covering the surface of the substrate with the above composition (II) to form the second layer, and a step of covering the surface of the second layer with the above composition (I) to form the first layer.
The present invention further provides a process for producing the above substrate having treated surface layers, which comprises a step of covering the surface of the substrate with the above composition (III) to form the third layer, a step of covering the surface of the third layer with the above composition (II) to form the second layer, and a step of covering the surface of the second layer with the above composition (I) to form the first layer.
The present invention further provides the above substrate having treated surface layers, wherein the substrate is a window glass.
Now, the present invention will be described in detail with reference to the preferred embodiments.
The substrate of the present invention is a substrate having at least two treated surface layers.
The first layer constituting the outermost layer among the treated surface layers is a layer formed by covering with a composition (I). The composition (I) contains (A) an organic silicon compound represented by the above formula (1). The composition (I) preferably contains (B) an acid and (C) an organic solvent, in addition to (A).
Firstly, (A) the organic silicon compound will be explained below.
(A) The organic silicon compound is represented by the above formula (1). In the formula (1), each of R1 to R3 is a methyl group or a group of the above formula (2), provided that at least one of R1 to R3 which are contained in one molecule is the group of the above formula (2), and all of R1 to R3 may be the group of the above formula (2). Particularly preferably, either one or both of R1 and R3 is the group of the above formula (2).
R1, a n number of R2""s and R3 may be the same or different. m is an integer of from 1 to 100 (preferably from 3 to 50), and n is an integer of from 0 to 10 (preferably from 0 to 5). m+n is an integer of preferably from 5 to 100, particularly preferably from 5 to 50. When m+n is at least 5, the water drop rolling property which will be described hereinafter is likely to be obtained, and when it is at most 100, workability in production of the substrate of the present invention tends to be excellent.
In the formula (2), A is a C2-10 bivalent hydrocarbon group which may have a linear structure or a branched structure, or an oxygen atom. Particularly preferred is xe2x80x94(CH2)qxe2x80x94 wherein q is an integer of from 2 to 6, particularly 2 or 3, or an oxygen atom.
R4 is a C1-10 monovalent hydrocarbon group, Q is an isocyanate group, a chlorine atom or an alkoxy group represented by OR5, provided that R5 is a C1-6 monovalent hydrocarbon group. R4 may, for example, be a methyl group, an ethyl group, a n-propyl group, an isopropyl group, a n-butyl group, an isobutyl group, a s-butyl group or a phenyl group. OR5 may, for example, be a methoxy group, an ethoxy group, a n-propoxy group, an isopropoxy group, an isopropenoxy group, a n-butoxy group or an acetoxy group. A p number of R4""s may be the same or different, and a (3-p) number of Q""s may be the same or different.
p is an integer of from 0 to 2, particularly preferably 0 or 1 in view of adhesion between the first layer and the second layer.
The composition (I) may contain one type of the compound (I), or may contain two or more types of the compounds (I).
Now, (B) the acid will be explained below.
(B) the acid is not particularly limited, and may optionally be selected depending upon the purpose. The acid to be used may, for example, be an inorganic acid such as sulfuric acid, hydrochloric acid, nitric acid or phosphoric acid, or an organic acid such as acetic acid, formic acid, p-toluenesulfonic acid or methanesulfonic acid. The acid may be added to the composition (I) as it is, or may be added in a form of an aqueous solution thereof with a purpose of e.g. accelerating the reaction as the case requires. The acid or its aqueous solution may preliminarily be added and mixed to prepare the composition (I) or it may be mixed to prepare the composition (I) immediately before use.
The content of (B) the acid in the composition (I) is preferably from 0.01 to 10 parts by weight based on 100 parts by weight of the compound (I). When it is at least 0.01 part by weight, an adequate effect by addition will be obtained, and when it is at most 10 parts by weight, the stability of the liquid tends to be excellent.
(B) the acid contributes to acceleration of the reaction and improvement in adhesion between the first layer and the second layer, which will be described hereinafter.
Now, (C) the organic solvent will be explained below.
The composition (I) may be used as it is, or may be diluted with (C) the organic solvent as the case requires, taking workability and the desired thickness of the first layer into consideration.
(C) the organic solvent is not particularly limited so long as it dissolves the other essential components. Preferred is an alcohol, a ketone, an aromatic hydrocarbon or a paraffin type hydrocarbon, and particularly preferred is a lower alcohol such as ethyl alcohol or isopropyl alcohol, or a paraffin type hydrocarbon. (C) the organic solvent is not limited to one type, and a mixture of at least two organic solvents having different polarity, vapor pressure, etc., may also be used.
The content of (C) the organic solvent in the composition (I) is preferably at most 100,000 parts by weight (particularly preferably at most 10,000 part by weight) based on 100 parts by weight of the compound (I). When it is at most 100,000 parts by weight, a uniform coating film is likely to be formed, and stable water drop removal property tends to be obtained.
The composition (I) may contain, in addition to the above components, an additive such as a metal oxide, a resin, a dye, a pigment, an ultraviolet absorber or an antioxidant, within a range of not impairing the purpose of the present invention.
By covering the surface of the second layer with the composition (I), the compound (I) contained in the composition (I) is chemically and/or physically bonded to the surface of the second layer. The compound (I) is a compound having at least one reactive group in its molecule, and it is considered that the compound (I) is bonded to the surface of the second layer mainly by a chemical reaction.
For covering the surface of the second layer with the composition (I), no special pre-treatment is required. Preferably, the first layer is formed immediately after the second layer is formed as mentioned hereinafter. The first layer is formed by coating the surface with the composition (I) by means of a known method such as brush coating, flow coating, spin coating, dip coating, squeegee coating, spray coating or hand coating, followed by drying in the air or in a stream of nitrogen. Depending upon the treating method, an excess component may result and impair the quality in appearance. In such a case, the excess component may be wiped off with a solvent or with a dry cloth to neaten the appearance. The thickness of the first layer to be formed by this surface treatment is not particularly limited, but it is preferably at most 100 nm (particularly preferably at most 50 nm) in view of economical efficiency. Further, the lower limit is a thickness of a monomolecular layer.
The second layer constituting an underlayer in contact with the first layer is a layer formed by covering with the composition (II) containing a fluorine-containing reactive silane compound (II) which forms a surface having a contact angle of at least 100xc2x0 to water.
The fluorine-containing reactive silane compound (II) which is an essential component for the composition (II) is a reactive silane compound having a fluorine-containing organic group, and is a compound which forms a surface having a contact angle of at least 100xc2x0 to water. Here, xe2x80x9ca compound which forms a surface having a contact angle of at least 100xc2x0 to waterxe2x80x9d is such a compound that when the surface of a washed soda lime glass substrate is completely covered with said compound so that the surface of the substrate is not exposed, the contact angle of the surface is brought to be at least 100xc2x0 to water after the covering.
In the compound (II), its reactive group is directly bonded to the silicon atom. The reactive group may, for example, be an isocyanate group, a halogen atom (excluding F), an alkoxy group, an acyloxy group, an alkoxy-substituted alkoxy group, an aminoxy group, an amide group, an acidamide group or a ketoxymate group. Among them, preferred are a C1-4 alkoxy group, an acyloxy group, an isocyanate group and a chlorine atom. The number of the reactive group bonded to one silicon atom is preferably at least two in view of affinity to the substrate or a treated surface layer constituting an underlayer in contact with the second layer.
The compound (II) is considered to present excellent performances such as water drop removal property, abrasion resistance, chemical resistance and weather resistance, due to reactivity of said reactive group. Further, it is possible to further improve such performances by selecting an organic group as mentioned hereinafter.
The compound (II) may be used as it is, or may be used as a hydrolyzate. The hydrolyzate of the compound (II) is a compound having e.g. a silanol group, formed by hydrolyzing a part or whole of the reactive groups of the compound (II) in water or in an acidic or alkaline aqueous solution, or a compound having at least two molecules condensed due to reaction of the silanol groups. The acidic aqueous solution may, for example, be an aqueous solution of e.g. hydrochloric acid, acetic acid, sulfuric acid, phosphoric acid, sulfonic acid or methanesulfonic acid.
The compound (II) is preferably a compound represented by the above formula (IIA) and/or (IIB). In the formula (IIA), each of Z1 and Z2 is an isocyanate group or a hydrolyzable group, and a (3-a) number of Z1""s and a (3-b) number of Z2""s may be the same or different. In the formula (IIB), Z3 is an isocyanate group or a hydrolyzable group.
Each of a and b is an integer of from 0 to 2, but is preferably at most 1, more preferably 0, in view of adhesion to the first layer and to the third layer as mentioned hereinafter or the substrate. Likewise, c is an integer of from 1 to 3, preferably 1.
Each of R6 and R7 is hydrogen or a C1-21 organic group, and a a number of R6""s and a b number of R7""s may be the same or different. Y is a bivalent organic group. At least one of the group of a a number of R6""s, a b number of R7""s and Y is a fluorine-containing organic group. R8 is hydrogen or a C1-21 organic group, provided that a c number of R8""s may be the same or different. At least one of a c number of R8""s is a fluorine-containing organic group.
The fluorine-containing organic group is bonded to the silicon atom preferably by means of a carbon atom having no fluorine atom (such as a carbon atom in a methylene group, an ethylene group or a propylene group).
In a case where Y is a bivalent fluorine-containing organic group, it is preferably a polyfluoroalkylene group, a polyfluorooxaalkylene group (one having at least one ether linkage in the middle of the carbon chain of an alkylene group) or a polyfluorothioxaalkylene group (one having at least one thioether linkage in the middle of the carbon chain in an alkylene group). Particularly preferred is a bivalent organic group having a polymethylene group (particularly dimethylene group) at each terminal which is bonded to the silicon atom, and a perfluoroalkylene group or a perfluorooxaalkylene group at the middle thereof. In this case, the carbon number of Y is preferably from 2 to 30, more preferably from 4 to 16.
In a case where Y is not a bivalent fluorine-containing organic group, preferred is an alkylene group, an oxaalkylene group or a thioxaalkylene group. In this case, the carbon number of Y is preferably from 2 to 30, more preferably from 2 to 12.
In a case where one of a a number of R6""s and a b number of R7""s is a monovalent fluorine-containing organic group, and in a case where one of a c number of R8""s is a monovalent fluorine-containing organic group, said monovalent fluorine-containing organic group is preferably a polyfluoroalkyl group, a polyfluorooxaalkyl group or a polyfluorothioxaalkyl group; or an organic group having one of the above groups and a hydrocarbon group such as an alkylene group bonded by means of an ester linkage, an ether linkage, a thioether linkage, an imino linkage, an amide linkage, a urethane linkage or another linkage (said organic group is bonded to the silicon atom at another terminal of the hydrocarbon group). The polyfluoroalkyl group and the polyfluorooxaalkyl group preferably have a perfluoro moiety and are bonded to the silicon atom by means of an alkylene group (particularly a dimethylene group). The perfluoro moiety in the monovalent organic group is preferably a perfluoroalkyl group, a perfluorooxaalkyl group or a perfluorothioxaalkyl group, having a carbon number of at least 3, particularly preferably a C3-16 perfluoroalkyl group.
In a case where an organic group having no fluorine atom is present in the compounds (IIA) and (IIB), said organic group is preferably a hydrocarbon group such as an alkyl group, an alkenyl group, a cycloalkyl group or an aryl group; a halogenated hydrocarbon group such as a chloroalkyl group; a (halogenated) hydrocarbon group having a hydroxyl group, an epoxy group, an amino group, a mercapto group, a carboxyl group or another functional group; or a (halogenated) hydrocarbon group having an ester linkage, an ether linkage, a thioether linkage, an imino linkage, an amide linkage, a urethane linkage or another linkage in the carbon chain. Among them, preferred are a methyl group and a long chain hydrocarbon group. As the long chain hydrocarbon group, preferred is a C4-20 alkyl group.
Now, specific examples of the compounds (IIA) and (IIB) will be shown below. In the following formulae, the symbols are as defined above. Further, Rf is a monovalent fluorine-containing organic group, n is an integer of from 2 to 16, and m is an integer of from 1 to 20. 
The composition (II) may contain one type of the compound (II), or may contain at least two types of the compounds (II).
The composition (II) may contain another compound or additive, in addition to the above components, depending upon the purpose. The additive etc. may be selected taking the reactivity and compatibility with the other components into consideration. It may, for example, be a non-fluorine type water repellent material such as a polydimethylsiloxane which is reactive at both terminals; ultrafine particles of a metal oxide such as silica, alumina, zirconia or titania; or a resin. Further, a dye, a pigment etc. may be incorporated in a case where coating is required. The amount of the additive etc. to be added may be a level of from 0.01 to 20 parts by weight based on 100 parts by weight of the compound (II), and an excessive addition may lower the water drop removal property, abrasion resistance etc. of the present invention.
The composition (II) may be used as it is, or may be diluted with an organic solvent as the case requires, taking workability and the desired thickness of the second layer into consideration.
The organic solvent to be used for the composition (II) may, for example, be an acetate, an aromatic hydrocarbon, a halogenated hydrocarbon, a ketone, an ether or an alcohol. However, in a case where the compound (II) has a highly reactive group such as an isocyanate group or a chlorine atom, a solvent having an active proton (a hydrogen atom in e.g. a hydroxyl group) is unfavorable. The organic solvent is not limited to one type, and a solvent mixture of two or more solvents having different polarity, vapor rate etc. may also be used.
The content of the organic solvent in the composition (II) is preferably at most 100,000 parts by weight based on 100 parts by weight of the compound (II). When it is at most 100,000 parts by weight, a uniform coating film is likely to be formed. The content of the organic solvent may optionally be determined taking moldability (workability) of the coating film, the stability, the thickness of the coating film and economical efficiency into consideration.
By covering with the composition (II), the compound (II) contained in the composition (II) is chemically and/or physically bonded to the surface of the third layer or the surface of the substrate. The compound (II) is a compound having at least one isocyanate group or a hydrolyzable group, which is a reactive group in its molecule, and the compound (II) is considered to be bonded to the surface of the third layer or the surface of the substrate mainly by a chemical reaction.
For covering the surface of the third layer or the surface of the substrate with the composition (II), no special pre-treatment is required. The formation of the second layer by covering with the composition (II) is carried out in such a manner that the surface is coated with the composition (II) by means of a known method such as brush coating, flow coating, spin coating, dip coating, squeegee coating, spray coating or hand coating, followed by drying in the air or in a stream of nitrogen. The thickness of the second layer to be formed by said surface treatment is not particularly limited, but it is preferably at most 50 nm in view of economical efficiency. Further, the lower limit is a thickness of a monomolecular layer.
The substrate of the present invention has at least the first layer constituting the outermost layer and the second layer constituting an underlayer in contact with the first layer, as mentioned above. Preferably, it further has a third layer constituting an underlayer in contact with the second layer, said third layer being a layer formed by covering with a composition (III) containing a reactive silane compound (III) containing no fluorine.
The reactive silane compound (III) containing no fluorine, as an essential component for the composition (III), is a reactive silane compound which has no fluorine atom.
In the compound (III), its reactive group is directly bonded to the silicon atom. The larger the number of reactive groups directly bonded to the silicon atom per silicon atom, the better. The compound (III) is preferably a compound represented by SiX4 (wherein X is an isocyanate group or a hydrolyzable group, and four X""s may be the same or different). Specifically, tetrachlorosilane, tetraisocyanatesilane or tetraalkoxysilane may be mentioned.
Due to reactivity of said reactive group, the compound (III) is strongly bonded mainly to the second layer and the substrate, and contributes to improvement in durability.
Further, the compound (III) may be used as it is, or may be used as a hydrolyzate by hydrolysis. The hydrolyzate of the compound (III) is a compound having e.g. a silanol group formed by hydrolyzing a part or whole of the reactive groups of the compound (III) in water or in an acidic or alkaline aqueous solution, or a compound having at least two molecules condensed by the reaction of the silanol groups. The acidic aqueous solution may, for example, be an aqueous solution of e.g. hydrochloric acid, acetic acid, sulfuric acid, phosphoric acid, sulfonic acid or methanesulfonic acid. Further, it is possible to add a metal oxide other than silica or its precursor compound to the compound (III) to obtain a mixed oxide layer or a composite oxide layer as the third layer.
The composition (III) may contain one type of the compound (III), or may contain two or more types of the compounds (III).
The composition (III) may contain another compound or additive, in addition to the above components, depending upon the purpose. The additive etc. may be selected taking reactivity and compatibility with the other components into consideration. As the additive etc., one to be used for the composition (II) may be used in a similar amount.
The composition (III) may be used as it is, or may be diluted with an organic solvent. As the organic solvent, one to be used for the composition (II) may be used.
By covering with the composition (III), the compound (III) contained in the composition (III) is chemically and/or physically bonded to the surface of the substrate. The compound (III) acts to significantly increase durability of the first and second layers, and at the same time, to increase adhesion to the substrate.
For covering the surface of the substrate with the composition (III), no special pre-treatment is required. However, depending upon the purpose, a pre-treatment may be applied. For example, 1) an acid treatment with hydrofluoric acid, sulfuric acid or hydrochloric acid, 2) an alkali treatment with an aqueous sodium hydroxide solution, or 3) a discharge treatment with e.g. plasma irradiation, corona irradiation or electron ray irradiation, may be carried out. Formation of the third layer by covering with the composition (III) is carried out by coating the surface with the composition (III) by means of a known method such as brush coating, flow coating, spin coating, dip coating, squeegee coating, spray coating or hand coating, followed by drying in the air or in a stream of nitrogen. The drying can adequately be conducted at room temperature. When heat drying is applied, the temperature and the time may be set taking the heat resistance of the substrate into consideration. The thickness of the third layer formed by said surface treatment is not particularly limited, and in a case where the substrate is e.g. a soda lime glass, the thickness may be at least 100 nm with a purpose of preventing elution of Na ions. The thickness is preferably at most 500 nm, whereby scratch marks are less likely to outstand even when there are scratches. The thickness is particularly preferably at most 100 nm. Further, the third layer may be extremely thin, and the lower limit is a thickness of a monomolecular layer.
The thickness of each layer to be formed can optionally be controlled by e.g. the concentration of the composition, coating conditions and heating conditions. The thickness of each layer is as mentioned above, but the entire thickness of the treated surface layers is preferably at most 1,000 nm (particularly preferably at most 100 nm) in view of economical efficiency.
In the present invention, the substrate on which the treated surface layers are provided, is not particularly limited. It may, for example, be an inorganic material such as a metal, a plastic, glass or a ceramic, an organic material, or a combination thereof (such as a composite material or a laminated material). Further, the substrate may be e.g. a metal having a layer of a deposited film, a sputtered film or a film obtained by e.g. a wet method, formed on its surface. For example, one having a coated surface such as a coated metal plate, or one having a treated surface layer such as a surface-treated glass, may be mentioned. Among them, a substrate made of a transparent material such as glass or a plastic, tends to present a remarkable effect of the present invention.
The shape of the substrate on which the treated surface layers are provided, is not limited to a flat plate. It may have an optional shape depending upon the particular purpose, such as one having a curvature over the entire surface or at a part thereof.
Now, the process for producing the substrate having treated surface layers of the present invention will be explained below.
The process for producing the substrate having treated surface layers of the present invention is not particularly limited. However, as a preferred production process, a process comprising a step of covering the surface of the substrate with the above composition (II) to form the second layer, and a step of covering the surface of the second layer with the above composition (I) to form the first layer, may be mentioned.
The step of covering with the above composition (II) to form the second layer and the step of covering the surface of the second layer with the above composition (I) to form the first layer are carried out as described in explanation of the compositions (I) and (II).
The above production process preferably comprises a drying step after the first layer is formed. The drying step may be carried out at room temperature, or heating may be carried out at a temperature of from 80 to 300xc2x0 C. for from 1 to 60 minutes. Drying at room temperature or drying by heating is selected depending upon e.g. purpose. The drying at room temperature is economically favorable as no special equipment has to be introduced. Particularly in a case where the object to be treated is incorporated into another article (e.g. a glass substrate mounted on an automobile), it is practically difficult to apply drying by heating, and the drying at room temperature is thereby selected. On the other hand, the drying by heating is favorable, since the drying rate tends to be high, and excellent durability tends to be obtained.
Further, in a case where the substrate of the present invention has a third layer constituting an underlayer in contact with the second layer, preferred is a production process which comprises a step of covering the surface of the substrate with the above composition (III) to form the third layer, a step of covering the surface of the third layer with the above composition (II) to form the second layer, and a step of covering the surface of the second layer with the above composition (I) to form the first layer.
The step of covering the surface of the substrate with the above composition (III) to form the third layer is carried out as described in the explanation of the composition (III). The step of covering with the above composition (II) to form the second layer and the step of covering the surface of the second layer with the above composition (I) to form the first layer are the same as in the case where the substrate has no third layer.
The above production process preferably comprises a heating step after the first layer is formed. The heating is carried out, for example, in the air at a temperature of from 80 to 250xc2x0 C. for from 5 to 60 minutes.
Further, a heating step may be carried out after the third layer is formed and before the second layer is formed. In such a case, heating is carried out, for example, at a temperature of at least 400xc2x0 C., preferably from 500 to 700xc2x0 C., for from 1 to 60 minutes. By heating, adhesion between the third layer and the substrate and density of the third layer will increase, and the durability will increase.
The substrate of the present invention is a substrate having at least two treated surface layers. Basically, the first layer formed by covering with the above composition (I) contributes to appearance of excellent water drop rolling property, the second layer formed by covering with the above composition (II) contributes to appearance of excellent water repellency, and the third layer formed by covering with the above composition (III) as the case requires, acts to strongly bond mainly the second layer to e.g. the substrate.
The effect of the present invention exceeds the effect expected in a case where materials having different functions are merely laminated. As mentioned above, the first layer formed by covering with the composition (I) is a silicone type coating film, and the second layer formed by covering with the composition (II) is a fluorine-containing silicone coating film. It is very difficult to coat the fluorine-containing silicone coating film having a low surface energy with a silicone coating film having a high surface energy, with conventional technique.
However, according to the present invention employing the constitution of the materials as mentioned above, such a coating becomes possible. The mechanism is not clear in detail, but it is considered that there is a strong interaction between molecules which can not conventionally be expected, between the material constituting the first layer and the material constituting the second layer, with a combination of selected materials for the compositions of the present invention. Part of the interaction is estimated to be mixing (interdiffusion) between the material constituting the first layer and the material constituting the second layer. In a case where the surface of the second layer is covered with the composition (I) as in the present invention, the contact angle of the surface of the first layer to water is high as compared with a case where the surface of a glass is directly covered with the composition (I). This is considered to be because the fluorine-containing reactive silane compound (II) in the material constituting the second layer having a large contact angle is diffused through the first layer in a process of forming the first layer, and a part thereof is exposed to the surface of the first layer.
Further, the first layer alone does not show a very high durable water repellency, but it shows an extremely high durability when coated on the surface of the second layer, and it is thereby considered that there is a synergistic effect which can not be expected with conventional technique, between the first layer and the second layer.
Namely, the concept of the layers in the present invention is such that the layers can be distinguished macroscopically, but microscopically, the border lines can not be strictly drawn, and a part or whole of the layers are mutually mixed with each other at the interface therebetween. In the present invention, due to such a layer structure, with respect to the water drop rolling property and durable water repellency depending on the material constituting the surface of the first layer, not only water drop rolling property derived from the composition (I) as the material constituting the first layer but also durable water repellency derived from the fluorine-containing reactive silane compound (II) as the material constituting the second layer is excellent.
As mentioned above, a water repellency agent intended to obtain surface characteristics of both a fluorine-containing silicone material and a silicone type material by mixing them, has conventionally been proposed. However, the fluorine-containing silicone material having a low surface energy tends to move outside the silicone type material having a high surface energy, and no desired water drop rolling property derived from the latter could be obtained.
In the pre sent invention, a substrate which is excellent in both water drop rolling property and durable water repellency, and which is excellent in water drop removal property, is realized by using the above compositions (I) and (II) as materials constituting the first and second layers, respectively, preferably by employing a predetermined production process.
The application of the substrate of the present invention is not particularly limited, but it is particularly useful for articles for transportation equipments. The articles for transportation equipments include window glasses (such as a windshield, a side glass and a rear glass), mirrors, display surface materials, instrument panels and other components (such as bodies and bumpers) in transportation equipments such as electronic cars, buses, trucks, automobiles, ships or aircrafts.
Such an article may be composed solely of the substrate of the present invention or may have the substrate incorporated therein. For example, the former may be a window glass for an automobile, and the latter may be a back mirror component for an automobile in which a glass mirror is incorporated.
With such substrates or articles, water drops on the surface will be repelled due to water drop removal property of the present invention. Especially, during driving of a transportation equipment, due to the interaction with the receiving wind pressure, water drops rapidly move on the surface and will not remain as water drops, whereby any adverse effect which may otherwise be induced by moisture, can be eliminated.
Especially in the application to a see-through portion such as a window glass, it becomes easy to secure a field of view due to dissipation of water drops. Namely, the substrate of the present invention is excellent in not only water drop rolling property but also water repellency, and e.g. raindrops attached to the surface will roll down as water drops, differently from a case of a surface having water drop rolling property but being poor in water repellency, water attached to which will roll down in a form of a film. Accordingly, it becomes easy to secure a field of view.
Further, the substrate of the present invention is excellent in not only initial water drop rolling property and water repellency but also abrasion resistance, weather resistance and boilproof resistance, due to the combination of the above first and second layers. Further, it is excellent also in chemical resistance, whereby it can be used at a region along the coastline or at a region where sea water is directly in contact.
When the substrate of the present invention has the third layer, the durability tends to be excellent. For example, when it is used for a windshield for an automobile, its performances can be maintained for from 3 to 5 years without separation or falling off of the first layer and the second layer.
In a case where the substrate of the present invention has no third layer, there is such an advantage that the first and second layers can easily be separated to newly form first and second layers on the occasion of repair.
Further, as the substrate is excellent in water repellency, in an environment where water drops usually freeze, no freezing of water drops takes place on the surface, or even if slight freezing takes place, the frozen drops can readily be defrosted. Further, there will be no substantial deposition of water drops, whereby the number of periodical cleaning operations can be reduced. Besides, the cleaning operation is very easy, such being advantageous also for the protection of good appearance.